When integrated circuitry is formed, contact openings are often formed through insulative material for establishing electrical communication with the integrated circuitry. Such contact openings are typically subsequently filled with conductive material, such as a metal or polysilicon, whereby electrical communication is established with the integrated circuitry.
Contact openings are often formed to be fairly narrow; and, it is desirable from a design standpoint to form the contact openings to have sidewalls which are as near vertical as possible. This helps to ensure that the contact area at the bottom of the contact opening is sufficiently large to desirably cover and/or expose conductive material with which electrical communication is desired. As aspect ratios, i.e. the height-to-width ratio, of contact openings increase, it becomes increasingly important to ensure that the dimension of the bottom of the contact opening is sufficiently large to provide adequate coverage for conductive material which is subsequently formed therein. For narrow contact openings, such is accomplished by maintaining the sidewalls of the contact opening as near vertical as possible.
Referring to FIGS. 1 and 2, two exemplary contact opening etch profiles are indicated generally at 100, 100a respectively. FIG. 1 shows a substrate 102 with a layer of insulative material 104 formed thereover. A masking layer 106 such as photoresist is formed over insulative material 104 and is subsequently patterned to define a contact opening pattern. Contact opening 108 is etched using an etch which is highly selective relative to masking layer 106. Hence, while a desirably high level of selectivity ensures that masking layer 106 remains over the substrate, the subsequent etch profile is unsatisfactorily tapered. FIG. 2 shows a substrate 100a in which like numbers from FIG. 1 have been utilized with the suffix "a". There, a contact opening 108a is etched through layer 104a using an etch with a comparatively lower degree of selectivity relative to an overlying masking layer (not shown). The lower degree of selectivity results in a contact opening profile with a more desirable degree of taper. Yet, the overlying masking layer can be completely removed, thereby undesirably opening up other substrate features to etching.
This invention arose out of concerns associated with providing methods of forming contact openings having sidewalls which are generally vertical within desired tolerances. This invention also arose out of concerns associated with providing methods for controlling the degree of taper of contact openings.